1. Field of the Invention
The present invention relates to a sealed battery having a safety feature in which the flow of a current is cut off and an internal pressure is released when a temperature of the battery is increased above an allowable level.
2. Description of the Related Art
A sealed battery can pose serious safety problems when an internal pressure thereof is increased above an allowable level as a result of being overcharged or otherwise abnormally operated. In particular, the sealed battery may explode under such conditions.
To solve the above problem, U.S. Pat. No. 4,943,497 discloses a cylindrical sealed battery having a safety device which is designed to cut-off the flow of a current when an internal pressure is increased above an allowable level.
That is, when the internal pressure of the battery is increased above an allowable level, an explosion-proof valve is deformed by the increased pressure so that an electrode lead welded on a projection of the explosion-proof valve is broken by a stripper, thereby cutting-off the flow of current to enhance the safety of the battery.
U.S. Pat. No. 5,418,082 discloses another sealed battery having means for cutting-off the flow of a current. The current cut-off means disclosed in the patent is designed such that a safety valve is deformed when internal pressure of the battery is increased, and a projection of the safety valve is disconnected from a metal membrane by the deformation of the safety valve, thereby cutting-off the flow of the current.
As additional safety means, each of the safety valves disclosed in the above two patents is provided with a safety groove which is designed to be broken when the internal pressure is increased above a predetermined safety level.
However, since each of the safety valves of the patents is designed to be operated only when the internal pressure is increased. Therefore, the batteries disclosed in the patents are still hazardous in that they may explode when a temperature of the battery is increased above an allowable level.
To solve this problem, a current control member which performs the cutoff of an electric circuit in response to an internal temperature of the battery has been proposed.
However, the current cutoff means, the safety valve, and the current control member complicate a structure of the battery and make necessary various parameters, making it difficult to exactly design the battery.
Therefore, the present invention has been made in an effort to solve the above described problems.
It is an objective of the present invention to provide a sealed battery having a safety feature which does damage parts of the battery when activated.
It is another objective of the present invention to provide a sealed battery which is simple in structure.
To achieve the above objectives, the present invention provides a sealed battery comprising a can for receiving an electric generator, a sealing member crimped on an opening of the can and connected to one of a positive electrode and a negative electrode of the electric generator, a gasket disposed between the can and the sealing member, a cover cap disposed on the sealing member with an insulating member disposed between the cover cap and the sealing member, a current control member disposed between the cover cap and the sealing member to cut-off a flow of current when a temperature of the battery is increased above an allowable level, and a shock absorber disposed between the cover cap and the current control member to prevent shock from being directly transmitted to the current control member.
The sealing member is designed to be broken when internal pressure of the battery is increased above an allowable level to prevent the explosion of the battery by exhausting an internal gas. The sealing member is provided with a safety groove for providing a mechanically weak portion.
The current control member is designed to be quickly increased in resistance within a temperature of 75-85xc2x0 C. A thickness of the current control member is less than that of the insulating member.
The insulating member is ring-shaped and the current control member is rectangular and disposed inside the ring-shaped insulating member. Alternatively, the current control member may be ring-shaped and disposed inside the ring-shaped insulating member.
The shock absorber is provided in the form of a metal foam or a metallic elastic member.